Types of Tumors
Benign tumors are abnormal growths that are no longer under normal regulation. They grow slowly, resemble normal cells, and are not cancerous. They grow only in one place and cannot spread or invade other parts of the body. They can however become harmful if they press on vital organs. Examples of benign tumors include skin moles, lipomas, hepatic adenomas.
These tumors are composed of embryonic, primitive, or poorly differentiated cells. They grow in a rapid, disorganized manner that is harmful to the body. They can also invade surrounding tissues and are become metastatic, initiating the growth of similar tumors in distant organs.
Cancer Types Based on Cell Genesis
Cancers can be classified based on cell origin.
- Carcinomas, the most common types of cancer, arise from the cells that cover external and internal body surfaces. Lung, breast, and colon are the most frequent cancers of this type in the United States.
- Sarcomas are cancers arising from cells found in the supporting tissues of the body such as bone, cartilage, fat, connective tissue, and muscle.
- Lymphomas are cancers that arise in the lymph nodes and tissues of the body's immune system.
- Leukemias are cancers of the immature blood cells that grow in the bone marrow and tend to accumulate in large numbers in the bloodstream.
Cancer Grading and Staging
Cancer staging (illustrated on the right for colon cancer) describes the extent of a person's cancer based on:
- The site of the primary tumor.
- Its size
- How far it has invaded into local tissues and structures
- Whether it has spread to regional lymph nodes.
- Whether is has metastasized to other regions of the body.
For additional information see the National Cancer Institute web page on Cancer Staging.
The microscopic appearance a cancer indicates its likely behavior and its responsiveness to treatment.
- Poorly differentiated cancers have highly abnormal cell appearance and large numbers of dividing cells and tend to grow more quickly, spread to other organs more frequently, and be less responsive to therapy than cancers whose cells have a more normal appearance.
- Based on these differences in microscopic appearance, doctors assign a numerical "grade" to most cancers.
- A low number grade (grade I or II) refers to cancers with fewer cell abnormalities than those with higher numbers (grade III, IV).
How Does Cancer Kill?
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